Pressure relief device for power transformer

ABSTRACT

A pressure relief device associated with power transformer apparatus of the fluid tank type, the relief device having a disk relief valve responsive to excessive gas pressure developing in the tank to relieve the tank of its excessive pressurized condition and to project a pin through a cover of the device to actuate an alarm switch, the pin being brightly colored and also serving as a visible warning signal.

United States Patent 1191 Johnson Oct. 21, 1975 [54} PRESSURE RELIEF DEVICE FOR POWER 3,100,502 8/1963 Ford 137/491 TRANSFORMER 3,113,172 12/1963 Barr 174/11 R 3,189,675 6/1965 Moore et al. 174/11 R Inventor: Wendell D. Johnson, Rochester, 3,217,082 11/1965 King etal 174/11 R [73] Assignee: Qualitrol Corporation, Fairport, Primary Examiner-Thomas J. Kozma N.Y. Attorney, Agent, or Firm-Stephen J. Rudy [22] Filed: Mar. 20, 1974 21] Appl. No.: 452,845 7] ABSTRACT R A pressure relief device associated with power trans- [52] Cl l74/1l 137529. 137/54319. former apparatus of the fluid tank type, the relief de- 6 336/105 vice having a disk relief valve responsive to excessive 511 im. cl. H01F 27/08 gas Pressurc developing in the tank relieve the tank [58] Field of Search 336/90 59 92 of its excessive pressurized condition and to project a 174/11 R 17 137/529 pin through a cover of the device to actuate an alarm switch, the pin being brightly colored and also serving [56] References Cited as a visible warning signal.

, UNITED STATES PATENTS 2 Claims, 1 Drawing Figure 2,904,616 9/1959 Koepke et al 174/11 R 4e 61 l I if 1 1 as o 5: 32

US. Patent Oct. 21, 1975 BACKGROUND OF THE INVENTION ond, the transformer tank will rupture spraying flaming oil over a wide area. The damage and fire hazard possibilities of this consequence are obvious, and it is imperative that measures be taken to prevent them.

Installations of a known type employ conventional slow acting pressure relief devices as the means to prevent the disasterous effects of a fault or short circuit; but it is most important to note that these conventional devices do not respond quickly enough to relieve an instantaneous pressure build-up.

The general object of this invention is to provide an improve pressure relief device'of such improved design that the sensing and relief of dangerous pressure increases in the fluid tank of a power transformer are accomplished immediately.-

In the present invention, a full. valve opening response within 2 milli-seconds of the development of a dangerous pressure increase has been calculated. This is accomplished through the particular structure of the relief device and the organized cooperative arrangement of its parts.

A feature of the relief device lies in the arrangement of its disk valve inoverlying relation to a pressure relief opening of a body member with which body member it has no contact other than a minimal seating contact with a gasket ring about the opening.

Another feature lies in the advantageous arrangement of an alarm switch atop the cover where it has a protected secure position, and has a non-complex association with an actuating pin' operable by opening movement of the disk valve. 4

In accordance with the invention, there is provided in an electrical power transformer apparatus including a tank having an opening in its top wall and containing cooling fluid. in which a transformer is immersed, a pressure relief device having an annular supporting body mounted to the wall of the tank over the opening, the body having an upper annular end wall defining an upper opening coaxial with the opening of the tank, a gasket ring seated in the end wall about the upper opening and protruding slightly above the end wall, a disk valve seated upon the gasket in coaxial relation thereto and to the upper opening, yieldable spring means arranged coaxially with the valve pressing the valve in sealing seated relation upon the gasket, the valve extending radially beyond the gasket in overlying spaced relation to the end wall and having no other contact with the supporting body apart from its contact with the gasket.

BRIEF DESCRIPTION OF THE DRAWING In order that theinvention may be fully understood and readily carried into effect, the same will be described by way' of an embodiment of the invention with reference to the accompanying drawing which:

is a cross sectional view of a pressure relief device embodying the invention, the pressure relief device being shown as mounted on the fluid tank of a power transformer and showing the relief valve thereof in its normal or closed condition.

DETAILED DESCRIPTION OF THE INVENTION Reference is now directed to the drawing wherein is shown a conventional fluid cooled electrical power transformer 10, to the tank 11 of which the improved pressure relief device 12 of the present invention has been applied.

The tank contains the usual cooling fluid in which the electrical component 14 of the transformer is immersed. The usual space between the fluid and the ceiling of the tank is provided.

The tank has an annular opening 15 in its top wall 16 over which an annular body member or support 17 of the device 12 is mounted and sealed relative to the tank by means of a mounting gasket 18.

- The body 17 of the device is rigidly held in sealed tight engagement with the top surface of the tank by means of bolts 19 passed through a radially extending base flange 22.

A bottom opening 23 of the body coincides in diameter with that of the tank opening 15. The body is turned radially inward at its top end to provide an upper gas escape opening 24 of a slightly narrower diameter than that of the opening 23.

The intumed upper portion of the body defines a level annular end wall 25 about the top opening. An annular groove 26 extending centrally about the surface of the end wall divides wall 25 into a pair of narrow parallel annular lands 27 and 28.

The inner land 27 is provided with an annular groove in which is seated a gasket ring 29, the surface of which projects slightly above the surface of both lands 27 and 28. A stiff valve disk 31 is held seated upon the gasket 29 and in sealing relation thereto by means of a spring load defined by a pair of coaxially arranged compression springs 32 and 33. The tank is, accordingly, normally sealed by the valve. The valve is made of light weight rigid sheet metal.

The springs are limited between the upper surface of the disk and an opposed wall of a protective spring retaining cover34. The cover is anchored rigidly to the base flange 22 portion of the body by means of a plurality of circumferentially spaced studs 35 and cooperating cap screws 36.

The cover has a substantially level top wall from which depends an annular protective skirt defined by an upper crown portion 39 which is offset inwardly by a radially extending annular land portion 41 from a lower skirt portion 40 of a greater diameter. The land portion 41 rests atop the spacing studs 35 and is rigidly fixed to the latter by means of the cap screws 36.

The studs serve not only to anchor the cover to the body 17 but also to space the cover axially upwardly and clear of the level of the seated valve. The lower skirt portion is relatively short in its axial dimension and is maintained by the studs at a suitable level above the valve. The relatively short axial dimension of the cover allows for economy of manufacture.

The valve is dished upwardly in its central area 42 and provides a flat service at the peak of the dished area upon which rests a switch actuating pin 44. The upper end of the pin extends with a slide fit through a bushing 45 to the outer surface of the cover. The bushing is fitted in a central aperture of the cover and is sealed by an O-ring against leakage down through the cover relative to the pin.

The pin is cooperable with a switch 46 in response to opening of the valve to sound a connected warning alarm. The switch which is of a conventional magnetic reed type is mounted atop the cover. For this purpose, the pin is preferably of an insulated plastics material.

The switch is of a conventional type having an aluminum block housing mounted atop the cover 34 by screws (not shown). It has a hole axially aligned with the pin and of a slightly greater diameter. A stainless steel switch cover 59 covers the hole and overlies the upper surface of the switch block. It is pivoted on a hinge pin 61 at one end; and its opposite end has a flange 62 depending in a vertical slot between a magnet 63 and reed switch contact means'at 64. A cable 60 connects the contacts contained in a cylindrical aluminum tube with an electrical alarm device (not shown). The switch has a normal condition (as shown) in which the disposition of the flange 62 disables the magnet from actuating the switch contacts and establishing a circuit to the alarm device. But when the valve is axially shifted by a pressurized gas condition in the transformer tank, the pin 44 is projected through the hole in the switch block causing the switch cover to be lifted and pivoted to the broken line position, thus enabling the magnet to effect closing of the switch contacts and operation of the alarm device.

The valve is provided with an annular ridge 47 on its upper surface about the outer edge of its dished area to define an aligning seat for the inner spring. An opposed annular ridge 48 on the inner back face of the cover provides a corresponding aligning seat for the opposite end of the spring.

The valve is of a diameter slightly greater than that of the end wall 25 of the body 17 so that it extends radially beyond the gasket 29 and slightly beyond and clear of the outer periphery of the body, the body being cylindrical. The valve may be provided with a short depending skirt49 which overhangs with a close clearance the outer periphery of the body. A clearance also exists below the valve where it extends beyond the gasket over the end wall of the body.

In this arrangement of the valve to the body, the valve has no contact with the body 17 apart from the minimal contact offered by the gasket 29 upon which it is seated.

The outer spring 33 limits upon the valve in overlying relation to the gasket 29 and is restrained in this position by an annular surface rib at 51 on the valve. The inner spring 32 limits upon the valve in overlying relation to the upper opening 24 of the body, being coaxial with this opening and of a smaller diameter.

Valve operation is effected when gaseous pressure developing within the tank 11 acting against the undersurface area of the valve defined by the diameter of the gasket seat 29 exceeds the design opening pressure established by the springs 32 and 33. As the valve cracks or moves upwards slightly from its seat, the

pressurized transformer gas then rapidly escapes over the gasket seat to theclearance 52 and annulus 26 beneath the marginal area of the valve and beyond the gasket. The gas pressure is then exerted over a substantially greater area of the valve and results in a greatly increased upwardly directed force upon the valve causing the latter to abruptly move axially upward to a fully open condition (broken line) limited by-the closed or solid height of the springs. The gas is then instantly relieved through the unimpeded radial open area defined by the fully open valve.

In the opening action of the valve, the switch actuating pin 44 is projected axially through the cover to the extent (broken line) permitted by a stop 54 at its lower end, the stop having cooperation with the bottom end of the bushing 45. As the pin moves upwardly, it swings the switch cover outwardly, as earlier mentioned, and actuates the alarm switch 46. This cooperative sliding arrangement of the pinrelative to the switch is of particular advantage in that operation of the switch by the rapid projection of the pin does not impede the desired swift opening of the valve. The switch has a desirable narrow block housing secured fast to the cover. It is to be noted that the switch is confined to a small central area of the cover and does not have any undesirable rigid projections beyond the cover that would otherwise be likely to be broken away. The pin is brightly colored so as to also serve as a visible signal when projected to its broken line position. The valve restores to its seated condition as the excessive tank pressure is relieved, but the projecting brightly colored pin is frictionally retained by the O-ring in the bushing 45' as an indicator of the action that had taken place.

What is claimed is:

L'The combination comprising an electrical power transformer including a tank having an opening in its top wall and containing cooling fluid in which a transformer element is immersed; a pressure relief device having an annular supporting body mounted to the wall of the tank over the opening, the supporting body having an upper annular end wall defining an upper opening coaxial with the opening of the tank, a gasket ring seatedin the end wall about the upper opening and protruding slightly above the level of the end wall, a disk.

valve seated upon the gasket in coaxial relation thereto and to the upper opening, yieldable spring means arranged coaxially with the valve pressing the valve in sealing seated relation upon the gasket, the valve extending radially beyond the gasket in overlying spaced relation to the end wall and having a peripheral flange depending in the seated condition of the valve in closely spaced surrounding relation to the supporting body, an annular crown cover mounted atop the supporting body in coaxial relation to the valve and in elevated spaced relation thereto, the cover providing an abutment to an upper end of the spring means, a plastics pin extending axially of the cover having a bottom end resting upon a central area of the valve and disposed with its opposite end through a bushing fitted in an axial aperture of the cover, the valve being movable axially against the spring means from the gasket in response to a predetermined pressure rise within the tank, the pin being movable through the bushing beyond the cover with theaxial movement of the valve; and an electrical alarm switch having a housing block mounted atop the cover provided with a hole registering with the pin through which hole the pin is movable,

the lip from the slot to activate the contacts, and the steel plate being pivotable to lift its lip from the slot upon projection of the plastics pin against the steel plate in moving through the hole.

2. The combination as in claim 1, wherein the pin is brightly colored. 

1. The combination comprising an electrical power transformer including a tank having an opening in its top wall and containing cooling fluid in which a transformer element is immersed; a pressure relief device having an annular supporting body mounted to the wall of the tank over the opening, the supporting body having an upper annular end wall defining an upper opening coaxial with the opening of the tank, a gasket ring seated in the end wall about the upper opening and protruding slightly above the level of the end wall, a disk valve seated upon the gasket in coaxial relation thereto and to the upper opening, yieldable spring means arranged coaxially with the valve pressing the valve in sealing seated relation upon the gasket, the valve extending radially beyond the gasket in overlying spaced relation to the end wall and having a peripheral flange depending in the seated condition of the valve in closely spaced surrounding relation to the supporting body, an annular crown cover mounted atop the supporting body in coaxial relation to the valve and in elevated spaced relation thereto, the cover providing an abutment to an upper end of the spring means, a plastics pin extending axially of the cover having a bottom end resting upon a central area of the valve and disposed with its opposite end through a bushing fitted in an axial aperture of the cover, the valve being movable axially against the spring means from the gasket in response to a predetermined pressure rise within the tank, the pin being movable through the bushing beyond the cover with the axial movement of the valve; and an electrical alarm switch having a housing block mounted atop the cover provided with a hole registering with the pin through which hole the pin is movable, the block being confined within the peripheral bounds of the cover, a magnet disposed in the block, a pair of switch contacts disposed in the block, a steel plate overlying the hole being hinged at one end to the block and having a lip at its opposite end depending in a normal condition in a slot between the magnet and the contacts, the magnet being adapted upon removal of the lip from the slot to activate the contacts, and the steel plate being pivotable to lift its lip from the slot upon projection of the plastics pin against the steel plate in moving through the hole.
 2. The combination as in claim 1, wherein the pin is brightly colored. 